The invention disclosed herein pertains generally to environmental contaminant discovery and treatment technology and, in particular, to a new and improved vapor sparging and collection well construction and a method of using the well in connection with monitoring ground water conditions.
Conventional sparging wells comprise a well shaft or a borehole made in the earth. One of two pipes extends from ground level down the shaft and terminates in an outlet to provide for injecting a pressurized gas such as air, oxygen or carbon dioxide into the water table for the purpose of developing gaseous bubbles that entrain, for example, contaminants, such as fuel oil, gasoline, lubricating oil, chlorinated hydrocarbons, transformer dielectric liquids and a host of other volatile chemical compounds that have permeated the soils at and above the water table as a result of ground spills or leaky tanks, for example. The sparging gas injected into the water table percolates up and through the capillary fringe and vadose soil and volatilizes the dispersed pressurized gas is distributed in the vadose zone above the water table in a slightly pressurized state. In the widely used conventional sparging wells, another pipe, that is, a suction pipe is also directed downwardly from the manway chamber at the upper part of the well. Since the conventional vapor sparging well shaft is an uncased hole drilled in the ground to the water table, a region above the water table in the well shaft and above the discharge end of the gas injection pipe, is sealed off with impervious grout. The grout extends upwardly in the well shaft to about the level where intake orifices of the suction pipe begin. This prevents the contaminated vapor from short circuiting up the well shaft and causes it to be diverted through the vadose zone to the suction pipe intake. Hence, contaminated vapor, as it is usually called, must follow a path through the vadose that is generally concentric to the well shaft before the gases can reach the suction pipe. This results in the suction or negative pressure having an effect in the vadose zone or ground at some radial distance from the well shaft. It is desirable for the negative pressure or suction effect to extend to the greatest area possible around the collection well.
One of the problems of a conventional and essentially standardized sparging well such as the one outlined above is that it lacks versatility. That is, it is not readily adaptable to operating in a solely pressure input mode, nor solely in a suction mode, and, therefore, it is not a good candidate for use in arrays or networks of interconnected wells wherein it would be highly advantageous to have one or more wells functioning in the gas sparging source mode, one or more wells acting in the contaminant collection mode and possibly other wells acting in sparging gas sourcing and vapor collection modes, alternately, or independently.
Another of the deficiencies of conventional sparging wells is that ground surface liquids can easily enter the well through the manway, which is a space at ground level for accessing the top of the well. Because of the vacuum or negative pressure condition created, these contaminants can be drawn down into the well borehole and render the well useless or ineffective. Another deficiency is the limited zone and area of influence, which is confined to the distance between the well pipe terminations and the points within the well vertically.